Insulated access doors for furnace walls are typically fabricated from concrete troweled over a wire screen reinforcement attached to the door structure, or from a plurality of heavy fire bricks attached by complex lug arrangements to the door structure. Both of these arrangements are expensive and their installation is time consuming since the resulting assembly may weigh well over a hundred pounds any may require the services of at least two mechanics over a period of days to complete the final installation. Also, the doors presently in use are somewhat brittle and are damaged quite easily if not handled with extreme care, thus adding to the difficulties.
Still another problem associated with these type doors is that they often require the installation of an additional fire brick protective shield at the face of the door to accommodate excess temperatures encountered in the furnace which would oxidize the retaining metal screen reinforcement. Of course, the installation and materials cost involved in such type of shields further adds to the expense involved.